1. Technical Field
This invention generally relates to optical systems for interferometric testing. More particularly, the present invention relates to an apparatus for aligning a reference reflector.
2. Discussion
As is generally known in the art of interferometry, there exists a very small acceptance angle wherein an image of the element or optical system to be tested can be captured for testing by an interferometer. Therefore, it is essential that the optical center of curvature of a reference reflector used in the testing procedure be positioned coincident with the focal point of the element or optical system to be tested. In this way, radiation returned from the reference reflector is reflected back to the interferometer wherein critical alignment may be performed. However, known interferometric testing systems do not possess means for accurately and conveniently locating the focal point of the element or optical system to be tested or means for positioning the reference reflector thereto. Moreover, such systems do not possess means for readily communicating to the optician the degree to which a reference reflector is misaligned.
Previously, alignment of the optical center of curvature of the reference reflector with the focal point of an element or optical system to be tested required a large degree of optician skill and experience. Conventional alignment of the reference reflector is accomplished by trial and error using pin holes, cards and other clues. These aids are not secured to the reference reflector and generally do not provide the optician with a large quantity of system feedback. Therefore, the optician must coordinate movement of two devices and rely on experience to quickly find the focal point of the element or optical system to be tested and align the optical center of curvature of the reference reflector thereto.
Furthermore, testing an element or optical system located within the interior of a complex system such as a telescope, high altitude camera or missile seeking system according to the prior art is cumbersome and inefficient. A reference reflector is often supported on a long wand and entered into the interior of the system. The wand is moved about until the reference reflector contacts radiation passing from the element or optical system to be tested. As is often the case, finding this radiation is generally by chance. After the radiation is located, the optical center of curvature of the reference reflector is positioned to the focal point of the element or optical system to be tested by optician skill and experience.